Steerability, among several attributes, is an important consideration in the manufacture and operation of an invasive catheter. In particular, when the operation of a catheter requires that it be advanced through portions of a patient's vasculature, the ability to steer the catheter along tortuous paths, and into selected branches of the vasculature, is of crucial importance. Further, in addition to having good steering properties, it may also be important to conform the catheter to a particular configuration as it is positioned in the vasculature. In either case, the steering and configuring of an invasive catheter requires that the distal tip of the catheter be articulated in a safe, predictable and controllable manner.
Several devices have been previously suggested for the purpose of steering a catheter through the vasculature of a patient. In the earlier mechanisms, such as the one disclosed in U.S. Pat. No. 1,060,665, that issued to Bell on May 6, 1913, for an invention entitled “Catheter”, the steerability of the catheter was provided for by using a pre-bent stiffening member in the catheter's distal end. Subsequently, more complex devices have relied on a pull-wire to deflect the catheter tip. In general, these mechanisms have variously included concentric or eccentric pull-wires that generate an eccentrically applied force on the tip of the catheter. For example, U.S. Pat. No. 4,456,017, which issued to Miles for an invention entitled “Coil Spring Guide with Deflectable Tip” incorporates a concentric core wire for this purpose. On the other hand, U.S. Pat. No. 4,586,923, which issued to Gould et al., uses an eccentric wire for the same purpose. Further, devices have also been proposed which will bias the deflection of a catheter tip in a predetermined plane. An example of such a device is disclosed in U.S. Pat. No. 4,886,067, which issued to Palermo. In the Palermo patent, such a bias is established by flattening the core wire.
Heretofore, as indicated by the examples given above, the steerability of a catheter tip has been primarily engineered by determining the direction in which a deflecting force should be applied to the tip. Accordingly, these earlier devices did not specifically incorporate structural aspects into the construction of a catheter's distal portion with a view toward using this construction as a functional aspect for tip deflection. Such a consideration, however, becomes more significant when, in addition to steerability, the configurability of a catheter in the vasculature of a patient is an important consideration.
In accordance with well known engineering applications, structures will predictably bend according to their shape of the structure and according to particular properties of the material, such as its modulus. By definition, a modulus is the ratio of stress to strain and, for a given material, is constant up to an elastic limit. Importantly, a modulus can be used as a measure of the deflection a material will experience under stress. Also, by definition, stress is the force per unit area acting on a material and tending to change its dimensions, i.e. cause a strain. With this in mind, it is evident to the skilled artisan that when two different materials are subjected to the same force, the materials will experience different strains according to their respective moduli. Further, when two different materials are incorporated into the same structural component of a system, a differential modulus is created for the component by the respective moduli that biases, or favors, a bending of the component according to the dictates of the material having the higher (flexural) modulus.
In light of the above, it is an object of the present invention to provide a device for steering a cardiac cryoablation catheter through the vasculature and in and around the heart of a patient that can be both steered and configured, as desired, while the catheter is in the vasculature and heart of a patient. Another object of the present invention is to provide a device for steering a cardiac cryoablation catheter through the vasculature and heart of a patient that relies on a differential modulus in the structure of the catheter's distal portion to steer and reconfigure the catheter. Still another object of the present invention is to provide a device for steering a cardiac cryoablation catheter through the vasculature and heart of a patient that is relatively easy to manufacture, is simple to use, and is comparatively cost effective.